In order to transport a large amount of heat generated in a semiconductor device and electronic equipment, a cooling method has been developed by which to achieve higher cooling performance by disposing a heat receiving unit outside the semiconductor device or the like and making a refrigerant flow inside the heat receiving unit. In particular, a cooling method based on a phase-change system has been developed by which a higher cooling effect can be obtained by boiling a liquid-phase refrigerant in a heat receiving unit.
In general, it is necessary to circulate a refrigerant between a heat receiving unit and a radiation unit in order to release heat drawn by a refrigerant to the outside. This makes a pump normally used. In contrast, it makes a pump unnecessary in a cooler using the phase-change system (hereinafter referred to as “a phase-change cooler”) to dispose a heat receiving unit in the lower part of the cooler and a radiation unit in the upper part of the cooler. Such a cooling structure employing the phase-change system utilizes the principle that the vapor-phase refrigerant accumulates upward in a vertical direction due to a density difference between a vapor-phase refrigerant and a liquid-phase refrigerant that arise.
An example of such a phase-change cooler is described in Patent Literature 1. An ebullient cooling device described in Patent Literature 1 includes a refrigerant tank to pool a refrigerant that boils by receiving heat from a heating element, and a radiation unit to liquefy the refrigerant vapor boiled in the refrigerant tank by a heat exchange with an external fluid. The refrigerant tank includes a vapor path through which the refrigerant vapor flows from a boiling space formed inside a heat-receiving surface to the radiation unit, and a liquid return path to return a condensed liquid liquefied in the radiation unit to the boiling space. It is configured to dispose recessively a surface close to the heating element of a lateral surface of the vapor path and a surface close to the heating element of a lateral surface of the liquid return path, on the side opposite to the heating element with respect to the heat-receiving surface.
If electronic equipment includes an element that is a vital portion of power consumption, the above-mentioned cooler is particularly effective in order to cool the element. If there are a plurality of heating elements, however, a plurality of those coolers are required.
An example of an electronic device using a plurality of coolers is described in Patent Literature 2. The electronic device described in Patent Literature 2 is configured to dispose a cooling system utilizing a thermosiphon for a plurality of central processing units (CPUs) of heat sources. Specifically, the condensers composing the cooling system are disposed aligning along a path of the air (the cooling wind) supplied from the outside by means of cooling fans.
The above-mentioned electronic device utilizes the cooling fans that are cooling means of other devices installed within a housing as the cooling means (the radiators) of the condensers composing the cooling system utilizing a thermosiphon. This makes it possible, they say, to cool down the CPUs as heat sources in the housing efficiently and certainly, without providing cooling fans for exclusive use, by the cooling system relatively simple and cheap, requiring no motive power of a pump to drive a liquid, and superior in the energy saving.
The related arts include the technologies described in Patent Literature 3 and Patent Literature 4.